Subordinate clause and main clause tense rule

Hi all,

I wanted to clarify about a rule for the tenses used in subordinate clause and main clause.
Are there any specific rules for the tenses used for these clauses?

For eg:

1) Using simple present for subordinate clause and future tense for main clause:

Because the population is denser there and the automobile is therefore inefficient as a means of transportation,a commuter rail system in a European city will usually be five times more efficient than will a system serving a comparable population in an American city

versus

2) Because the population is denser there and the automobile is therefore inefficient as a means of transportation,a commuter rail system in a European city is usually five times more efficient than is a system serving a comparable population in an American city

Is there any error in the second sentence?

Appreciate your help!


Thanks,
Andy